The present invention relates to a dielectric ceramic composition exhibiting a high dielectric constant, capable of sintering in a short time, at a sintering temperature of 800.degree. to 1000.degree. C., in the atmosphere, a neutral atmosphere or a reducing atmosphere.
As materials exhibiting a high dielectric constant suitable for use in ceramic capacitors which are progressively reduced in size and enlarged in capacity, materials mainly composed of barium titanate have been hitherto employed. However, it is necessary to sinter these materials in the atmosphere at a high temperature of about 1300.degree. C. Therefore, when fabricating laminate ceramic capacitors, expensive noble metals such as platinum and palladium are indispensable as the electrode materials, and in particular along with the trend for increasing capacity, the cost of the internal electrode material has pushed up the material cost.
Recently, it has been attempted to lower the cost of laminate ceramic capacitors by, inter alia, the following two methods. One method involves making barium titanate material resistive to reduction, and sintering it in an atmosphere of a low oxygen partial pressure, thus making it possible to use an inexpensive base metal as the electrode material. The other method involves sintering at a low temperature of about 1000.degree. C. a silver-palladium alloy electrode material and a lead dielectric material and inexpensive silver.
On the other hand, in electronic appliances where reduction in size and enhancement of reliability are demanded, the hybrid IC of a high packaging density is promoted, and the demand for a thick film capacitor is mounting to replace the conventional chip capacitor. To fabricate this thick film capacitor, a dielectric material capable of sintering at a low temperature and in a short time is required, and the lead dielectric is used mainly as this material. Therefore, as the material applicable to both increasing the capacity of a laminate chip capacitor and providing a thick film capacitor, the lead dielectric is being developed intensively.
A PbTiO.sub.3 - Pb(Mg.sub.1/3 Nb.sub.2/3)O.sub.3 - Pb(Ni.sub.1/2 W.sub.1/2)O.sub.3 solid solution and a PbZrO.sub.3 - Pb(Ni.sub.1/3 Nb.sub.2/3)O.sub.3 - Pb(Ni.sub.1/2 Wi1/2)O.sub.3 solid solution are compositions exhibiting a high dielectric constant which can be sintered in the atmosphere at 1100.degree. C. or a lower temperature, as disclosed in Japanese Patent Laid-Open Nos. 61-155249 and No. 61-155248, but it is necessary to maintain the sintering temperature for several hours in order to heighten the dielectric constant and to obtain sintered material having a sufficient density. On the other hand, when fabricating a thick film capacitor for a hybrid IC, a low temperature and a short sintering time is indispensable, and these dielectric materials are not sintered completely under such conditions, and therefore the desired characteristics are not obtained. Still worse, due to the effects of heat in a neutral or reducing atmosphere over a long period of time, oxygen defects are likely to occur in the dielectric ceramics, which lead to practical problems such as lowering of the dielectric constant and reduction of insulation resistance.